The present invention relates to a tablet printing machine.
Generally, tablet printing machines comprise a design roll (gravure roll), a transfer roll and a feed roll which are rotated continuously at a high speed Code numbers are engraved in the surface of the design roll, the lower portion of which is held placed in an ink fountain. When the design roll moves past the interior of the ink fountain, the ink adhering to the roll surface is scraped off by a doctor blade except at the recessed portions engraved with the code numbers, and only the ink remaining in the recessed portions is transferred to the surface of the transfer roll which is made of rubber. The ink transferred to the transfer roll surface is then transferred to the surfaces of tablets held on the feed roll. At this time, particles of tablets and coating fragments thereof gradually accumulate on the transfer roll surface, while broken pieces of tablets, soils in the ink, etc. are likely to adhere to the transfer roll surface. The extraneous substances and ink soils thus adhering to and soiling the transfer roll surface produce faulty prints, so that there arises a need to clean the roll surface. However, the kind of soils on the surface of the transfer roll and the progress of soiling with time differ with the shape of tablets, formulation of coating agents, etc., while tablets break accidentally. Accordingly, the transfer roll surface will not be fully cleaned when cleaned only periodically. Although the operator usually observes with the unaided eye changes in the soiling surface of the transfer roll during operation, the roll surface rotating at a high speed is extremely difficult to monitor for accurate checking of soiling. In recent years, investigations are under way in various fields for the detection of soils on the surface of articles by an image processing system, whereas even the image processing system encounters difficulties in detecting soils on the surface which is moving at a high speed. Moreover, the processing software is very costly to develop.
The extraneous matter and ink soils adhering to the transfer roll surface is removed therefrom conventionally by cleaning the surface with a cleaning material impregnated with a cleaning liquid and manually held by the operator against the rotating roll surface during an interruption of printing operation. However, this procedure requires much time and involves safety problems. It is therefore desired to automatically clean the roll, but the following problems still remain to be solved for realizing the automation. In automating cleaning of the printing machine transfer roll, a cleaning unit including a mechanism for automatically pressing a cleaning material or cleaner against the roll surface must be incorporated into the printing machine within a limited space available. Further since the cleaning liquid soiled by cleaning is likely to conversely soil the roll, the cleaner needs to be replaced frequently and is therefore cumbersome to handle.